(ABC NEWS) -- At least five Republican senators all say they will oppose a key procedural vote expected this week on the GOP health care plan that will repeal and replace Obamacare -- a move that would effectively block the GOP health care bill from reaching the floor.

Sens. Susan Collins of Maine, Rand Paul of Kentucky, Dean Heller of Nevada, Mike Lee of Utah and Ron Johnson of Wisconsin have signaled they will vote no, or plan to vote no, if there are no changes made to the legislation ahead of the vote, expected Tuesday or Wednesday.

With only 52 seats in the Senate, Republicans can only afford two defections and still advance the health care bill.

This news comes on the heels of the Congressional Budget Office (CBO) report released Monday that estimates that 22 million more Americans will be uninsured by the end of the next 10 years under the Senate Republican health care plan than under current law, with 15 million more uninsured persons in the next year alone.

Sen. Collins, who earlier today had been uncommitted on advancing the health care measure, tweeted tonight: “I want to work w/ my GOP & Dem colleagues to fix the flaws in ACA. CBO analysis shows Senate bill won't do it. I will vote no on mtp.” MTP refers to Motion to Proceed, the procedural vote that brings up a bill on the floor for consideration.

Before the Senate can begin debate on most legislation, the senators must either unanimously agree to consider it or the majority leader must offer a “motion to proceed” to consideration of that bill.

The 22 million figure, which is only a slight improvement from the CBO's estimate of the health care bill passed by the House of Representatives in May, comes in the office's analysis of the Better Care Reconciliation Act, a draft of which was released last week.

The act, which faces staunch opposition from Democrats, could further result in a reduction of the cumulative federal deficit by $321 billion by 2026, largely due to cuts in Medicaid spending, according to the CBO's report.

“I won’t vote to proceed unless the bill changes,” Sen. Paul told reporters Monday. He wants the GOP legislation to go even further in rolling back certain Obamacare measures.

Paul said he spoke with President Trump Sunday evening, but lamented over the lack of communication he has received from GOP leadership.

“I had a long conversation with the president last night and I think he's open to negotiations, but we have not had any word from anyone in Senate leadership,” he said.

“No one from leadership has reached out to us,” he added. "I would highly doubt I would support it,” Sen. Ron Johnson told reporters of the motion to proceed. Johnson has been adamant in recent days to hold off on a vote on the bill, which leadership is pushing to happen before the July 4 recess.

Sen. Lee through a spokesman confirmed to ABC News that he also intends to vote "no" on the procedural vote unless changes are made.

On Friday, Sen. Dean Heller said he would not support the bill as it is during a press conference with the Nevada governor.

Is there room to negotiate?

Moments after the CBO score was released Sen. Lindsay Graham, R-South Carolina, said the vote was getting tougher by the minute.

“How you put all this together and get to 50 is going to be very tough and the CBO score doesn't help any. If you had problems with the bill before, you're probably going to have more problems now,” he said.

Graham said if senators are considering voting no because of how it will affect their states, then stick to it and vote no.

“I don't believe in this running off a cliff like our Democratic friends did. They got this herd mentality where we gotta pass this bill or else,” he said.